This invention relates to photographic products and processes for the formation of images in color or black-and-white by diffusion transfer processing. More particularly, it relates to photographic products adapted to the provision of a diffusion transfer image retained within a permanent laminate having at least one developed silver halide emulsion and viewable through a transparent support against a reflecting background.
Diffusion transfer photographic products and processes have been described in the art and details relating to such products and processes can be found, for example, in U.S. Pat. Nos. 2,983,606; 3,415,644; 3,415,645; 3,415,646; 3,473,925; 3,482,972; 3,551,406; 3,573,042; 3,573,043; 3,573,044; 3,576,625; 3,576,626; 3,578,540; 3,579,333; 3,594,164; 3,594,165; 3,597,200; 3,647,437; 3,672,486; 3,672,890; 3,705,184; 3,752,836; 3,857,865; and in British Pat. No. 1,330,524.
Essentially, diffusion transfer photographic products and processes involve film units having a photosensitive system including at least one silver halide layer usually integrated with an image-providing material. After photoexposure, the photosensitive system is developed to establish an imagewise distribution of a diffusible image-providing material, at least a portion of which is transferred by diffusion to an image-receiving layer capable of mordanting or otherwise fixing the transferred image-providing material. In some diffusion transfer products, the transfer image is viewed by reflection after separation of the image-receiving element from the photosensitive system. In other products, however, such separation is not required and the transfer image is viewed against a reflecting background, usually provided by a dispersion of a white, light-reflecting pigment such as titanium dioxide.
A number of photographic products and processes have been proposed for providing photographs comprising the developed silver halide emulsion(s) retained as part of a permanent laminate, with the desired image being viewed through a transparent support against a reflecting background. In such photographs, the image-carrying layer is separated from the developed silver halide emulsion(s) in the laminate by a light-reflecting layer, e.g., a layer containing titanium dioxide, positioned between the image-carrying layer and the developed silver halide emulsion(s). Diffusion transfer photographic products providing an image viewable without separation against a reflecting background in such a laminate have been referred to in the art as "integral negative-positive film units" and such units have been of two general types.
Integral negative-positive film units of a first type are described, for example, in the above-noted U.S. Pat. No. 3,415,644 and include appropriate photosensitive layer(s) and image dye-providing materials carried on an opaque support, an image-receiving layer carried on a transparent support and means for distributing a processing composition between the elements of the film unit. Photoexposure is made through the transparent support and image-receiving layer and a processing composition which includes a reflecting pigment is distributed between the image-receiving and photosensitive components. After distribution of the processing composition and before processing is complete, the film unit can be, and usually is, transported into light. Accordingly, in integral negative-positive film units of this type, the layer provided by distributing the reflecting pigment must be capable of performing specific and critical assigned functions. Until processing is complete, the distributed reflecting layer must be able to provide at least partial protection against further exposure of the photoexposed element. At the same time, however, the layer must be sufficiently permeable to permit effective transfer of image-forming materials from the photoexposed photosensitive layer(s) to the image-receiving layer. Moreover, after transfer, the layer must provide a reflecting background of suitable efficiency for viewing the image transferred to the image-receiving layer. Also, in film units of this type, the reflecting layer masks the developed photosensitive layer(s).
Integral negative-positive film units of a second type, as described, for example, in U.S. Pat. No. 3,594,165, include a transparent support, carrying the appropriate photosensitive layers and associated image dye-providing materials, a permeable opaque layer, a permeable light-reflecting pigment-containing layer, an image-receiving layer viewable through a transparent support against the light-reflecting layer, and means for distributing a processing composition between the photosensitive layer and a transparent cover or spreader sheet. Additionally, integral negative-positive film units of this second type include an opaque processing composition which is distributed after photoexposure to provide a second opaque layer which can prevent additional exposure of the photosensitive element. In film units of this second type, exposure is made through the transparent cover sheet. After distribution of the processing composition and installation of the second opaque layer, this type of film unit can also be transported into light before processing is complete. Accordingly, in film units of this second type, the light-reflecting pigment-containing layer may also perform the critical assigned functions of providing at least partial protection for the photoexposed element until processing is complete, but again, this layer must permit effective transfer of image-forming material to the image-receiving layer. Also, like the film units of the "first type", the layer must provide a suitable reflecting background for viewing the dye image transferred to the image-receiving layer. Moreover, effective masking of the developed photosensitive layer(s) must also be achieved for film units of this "second type".
In many known integral negative-positive film units, auxiliary opacification systems have been used in combination with light-reflecting layers and light-reflecting layer materials. These auxiliary opacification systems are designed to cooperate with the reflecting layer and/or reflecting layer materials to provide sufficient opacity to prevent further exposure of the film unit through the reflecting layer during processing of the film unit in light.
U.S. Pat. No. 3,647,437, for example, describes an auxiliary opacification system that has been extensively in commercial integral negative-positive film units of the first type, e.g., film units of the type described in U.S. Pat. No. 3,415,644. That auxiliary opacification system essentially involves a pH-sensitive, optical filter agent which can absorb light at one pH but is rendered less light-absorbing at another pH. As disclosed in U.S. Pat. No. 3,647,437, the optical filter agent is usually dispersed in the film unit's processing composition together with a light-reflecting pigment. In turn, the processing composition is integrated with elements of the film unit so that the composition can be distributed between the photoexposed photosensitive layer(s) and the image-receiving layer. Accordingly, after distribution of the processing composition, an opaque layer comprising the reflecting pigment and the optical filter agent is provided and the opaque layer covers a major surface of the photoexposed layer(s). At least during the initial stages of development, the pH sensitive optical filter agent absorbs light and cooperates with the reflecting pigment to provide a degree of opacity sufficient to prevent photoexposure through the layer. As transfer of image-forming material proceeds, the light-absorbing capability of the pH-sensitive optical filter agent is reduced until the agent becomes substantially non-light absorbing and its opacification function is terminated. When transfer of image-forming material is complete, the reflecting layer comprising the reflecting pigment and the non-light absorbing filter agent, provides a reflecting background for viewing the dye image.
While the utilization of pH-sensitive optical filter agents in integral negative-positive film units as described is effective to provide the requisite opacification to permit in-light development of photoexposed silver halide emulsions in such laminate structures, there are certain notable disadvantages associated with such utilization. For example, such pH-sensitive optical filter agents tend to be large molecular species and may inhibit the rate of diffusion therethrough of image-forming materials, e.g., image-forming dyes. In addition, such pH-sensitive optical filter agents are highly colored in their light-absorbing or opacifying mode and, thus, image formation will be observed to occur against such colored background. It may be preferred to some consumers that the image formation appear to emerge from a white or nearly white background and the utilization of a reflecting layer providing such a white background in a photographic laminate may be preferred to such consumers.
In addition to pH-sensitive optical filter agents, carbon has also been used as an auxiliary opacification agent for integral negative-positive film units. For example, dispersions of reflecting pigments and small amounts of carbon, about 1 part of carbon to about 100 to 500 parts of reflecting pigment, have been proposed to provide light-reflecting layers for film units of the type described in U.S. Pat. No. 3,415,644. Similarly, carbon has been employed as an auxiliary opacification agent in integral negative-positive film units of the type described in the aforesaid U.S. Pat. No. 3,549,165. Film units of this type have a permeable reflecting layer as an integral layer of the film unit and a layer of light-absorbing pigment, usually carbon, positioned between the light-reflecting layer and the photosensitive element to provide additional opacification for protection of the photosensitive element during processing and for effective masking of the photoexposed and developed element.
U.S. Pat. No. 3,647,435 describes still another integral negative-positive film unit which uses carbon as an auxiliary opacification agent. In the film units described in such patent, a reflecting layer is generated in situ from a preformed layer of reflecting pigment precursor, the processing composition containing dispersed carbon. After dye transfer is complete, the generated light-reflecting pigment layer provides a reflecting background for viewing the dye image and masks the distributed carbon.
The utilization of dispersed carbon in a processing composition or a preformed layer of carbon in an integral negative-positive film unit, while effective to provide efficient opacification, may detract from the ability to provide a white reflecting background for viewing of the desired photographic image. Additionally, the utilization of a preformed carbon layer requires that such layer be integrated into a diffusion transfer unit containing a plurality of other sheet or coated elements required or customarily utilized in the manufacture of such film units.
It is an object of the present invention to provide photographic diffusion transfer products and processes effective for the provision of a diffusion transfer image as part of a permanent laminate and viewable through a transparent element against a light-reflecting layer.
It is another object of the present invention to provide a light-reflecting layer in such products and processes effective to provide the requisite opacification to permit in-light development of the photoexposed silver halide emulsion(s) thereof while providing light-reflecting properties suitable for viewing of the desired transfer image.
Yet another object of the present invention is to provide a light-reflecting layer useful for the provision of opacification and light-reflecting properties without the required employment of additional opacification agents or systems.
Still another object of the present invention is to provide photographic diffusion transfer products and processes of the integral negative-positive type effective for the provision, in a unitary and readily integrated light-reflecting layer, of opacification sufficient to permit in-light development and light-reflecting properties sufficient for background viewing of a desired transfer image.
Other objects will become apparent from the description appearing hereinafter.